1. Field of the Invention
The present invention relates to an inkjet recording apparatus using a line-type recording head.
2. Description of the Related Art
A line-type inkjet recording apparatus uses a line-type recording head in which a nozzle array extends over the entire width of a recording region. In a nozzle that is not frequently used in the nozzle array, a volatile component of ink evaporates, and this increases the ink viscosity. If the increase in ink viscosity further continues, there may be a risk that the nozzle cannot discharge ink (clogging).
To overcome this problem, attempts have been made to suppress evaporation of the volatile component of ink by supplying humidified gas near the nozzles in the recording head for the purpose of moisture retention. For example, Japanese Patent Laid-Open No. 2006-44021 (Patent Document 1) discloses a recording apparatus having a structure for supplying humidified gas into a gap between a recording head and a sheet.
A line-type recording apparatus has two different regions, that is, a region where a conveyed sheet faces a nozzle array of a recording head (hereinafter referred to as a conveying region) and a region where a conveyed sheet does not face the nozzle array (hereinafter referred to as a non-conveying region). Since sheets of various sizes (widths) are used in the recording apparatus, the relationship and ratio between the conveying region and the non-conveying region change in accordance with the size of the sheet to be used.
The gap through which humidified gas flows is narrower in the conveying region by an amount corresponding to the thickness of the sheet than in the non-conveying region. For this reason, the flow rate of humidified gas is lower in the conveying region than in the non-conveying region, and the effect of suppressing evaporation of ink in the nozzles is also smaller in the conveying region than in the non-conveying region. In addition, when a highly hygroscopic sheet, such as a paper sheet, is used, the sheet itself absorbs moisture from the humidified gas during conveyance. Hence, the effect of suppressing ink evaporation in the conveying region further decreases.
Ink does not evaporate from the nozzles that are included in the conveying region and are used for image recording. However, depending on an image to be formed, in the conveying region, there may be a nozzle whose use frequency is extremely low. Such a nozzle in the conveying region whose use frequency is extremely low may be clogged by ink evaporation. Patent Document 1 described above does not take this problem into consideration.